Thumb screw with overload release means



May 15, 1956 P. D. CORNELIUS 2,745,303

THUMB SCREW WITH OVERLOAD RELEASE MEANS Filed June 25, 1954 4 Sheets-Sheet 1 P\ V340 38 G8 rzo 3G55 INVENTOR. QuL 0. Co2/venus May 15, 1956 P. D. CORNELJUS THUME SCREW WITH ovEREoAD RELEASE MEANS 4`Sheets-Sheet 2 Filed June 25. 1954 TCL 0E r WM j V0. D. L aU". PM

May l5, 1956 Filed June 25,

P. D. CORNELIUS THUMB SCREW WITH OVERLOAD RELEASE MEANS AAA 4 Sheets-Sheet 3 IN V EN TOR. nuL 0. Coe/venus @tang/M5 May 15, 1956 P. D. CORNELIUS THUMB SCREW WITH OVERLOAD RELEASE MEANS Filed June 25, 1954 4 Sheets-Sheet 4 INVENToR.

PQuL D. Co2/venus United States Patent i THUMB SCREW WITH OVERLOAD RELEASE MEANS Paul D. Cornelius, Burbank, Calif., assigner to Vlier Engineering, Inc., Los Angeles, Calif., a corporation of California Application June 25, 1954, Serial No. 439,295

17 claims. (c1. :s1-52.4)

The present invention relates generally to the eld of metal working and more particularly to a novel thumb screw with overload release utilized to clamp a workpiece in position to be machined.

In the field of metal machining it is common to clamp a workpiece within a jig or fixture whereby the workpiece may be machined. Where the workpiece is of a fragile or relatively easilyV deformed nature the pressure exerted thereagainst must not exceed a certain limit. To this end it has been heretofore proposed to utilize so called torque thumb screws for holding lthe workpiece. The heretofore-proposed torque thumb screws have generally consisted of a screw member which is threadedy through a complementary threaded bore in the jig or fixture so that its front end may engage the workpiece. The rear end of the screw member mounts a head that is manually rotated for effecting a concurrent rotation of the screw member. interposed between the rear end of the screw member and the head are torque responsive means that serve to disengage the head member from the screw member when the resistance of the latter against rotation reaches a predetermined value, such resistance against rotation resulting from the engagement of the front end of the screw member with the workpiece.

Although these heretofore-proposed devices are gen erally satisfactory in operation where the resistance against rotation developed between the screw member and the threaded bore of the jig or fixture is of a known value, this value is subject to uctuation. Thus, this value may vary within wide ranges depending upon the tightness of fit between the mating surfaces of the pressure screw and the threaded bore, the presence or absence of foreign matter on these mating surfaces, the state of lubrication existing between such surfaces, and the condition of the threads of these mating surfaces. Accordingly, inasmuch as these heretofore-proposed torque thumb screws rely upon the resistance of the pressure screw against turning, they cannot always provide -an accurate indication of lthe axial force being applied by the pressure screw against a workpiece.

lt is a major object of the present invention to provide a novel and improved workpiece engaging device wherein the axial force applied against the workpiece is utilized to control the release of the head from the screw member. With this arrangement, the sensing of the end pressure being exerted by the workpiece engaging device is independent of the thread friction generated between the device and the threaded bore of the workpiece-holding jig. This workpiece engaging device is hereinafter termed a thumb screw with overload release.

Another object is to provide a pressure screw of the aforedescribed nature which is fool-proof in use even when operated by a comparatively unskilled workman.

A further object is to provide a thumb screw with overload release that is simple in design and rugged of construction whereby it may provide a long and troublefree service life.

2,745,303 Patented May 15, 1956 ICC An additional object of the invention is to provide a thumb screw with overload release of the aforedescribed nature which may replace existing torque thumb screws without requiring modification of the jigs and fixtures already developed for use with the latter.

Yet a further object of the invention is to provide a thumb screw with overload release that is economical of construction.

Another object is to provide a thumb screw with overload release which is adapted to withstand vibration, shock and the presence of foreign matter without losing its accuracy.

These and other objects and advantages of the present invention will become apparent from the following detailed description, when taken in conjunction with the appended drawings wherein:

Figure 1 is a perspective view showing a workpiece being held within a jig by means of a pair of thumb screws embodying the present invention;

Figure 2 is a central sectional view of a lirst form of thumb screw embodying the present invention;

Figure 3 is a vertical sectional View taken on line 3-3 of Figure 2;

Figure 4 is a fragmentary central sectional view of the thumb screw of Figure 2 showing certain of its parts in a different position;

Figures 5 and l6 are horizontal sectional views taken on line 5-5 of Figure 2 and showing the mode of operal tion of said thumb screw;

Figure 7 is an exploded view of the parts of said thumb screw;

Figure 8 is a central longitudinal sectional view of a second form of thumb screw embodying the presen-t invention;

Figure 9 is a vertical sectional View taken on line 9 9 of Figure 8;

Figure 10 is a fragmentary central longitudinal sectional view showing the parts of the second form of thumb screw disposed in a different position;

Figure 11 is a central longitudinal sectional view of a third form of thumb screw embodying the present invern tion;

Figure 12 is a vertical sectional view taken on line 12--12 of Figure 11;

Figure 13 is a central longitudinal sectional view showing the parts of said third form of thumb screw disposed in a dierent position;

Figure 14 is a perspective view of a detail of the thumb screw of Figures 11, 12 and 13;

Figure 15 is a central longitudinal sectional view of the preferred form of thumb screw embodying the present invention; K

Figure 16 is a vertical sectional view taken on line 16-16 of Figure 15;

Figure 17 is an enlarged perspective View showing a detail of the thumb screw of Figures 14, 15 and 16;

j Figure 18 is a fragmentary central longitudinal sectional view showing the parts of said preferred embodiment disposed in a different position; and

Figure 19 is an enlarged sectional View showing a dertail of Figure 18.

Referring to the drawings, and particularly Figure 1 thereof, a workpiece W is shown clamped within a jig or fixture by means of a pair of thumb screws with overload releases P embodying the present invention. The side walls 20 of the jig J are formed with threaded bores 22 wherein the thumb screws P are threadably secured with their front ends in engagement with bifurcations 24 and 26 of the workpiece W. With this arrangement, the workpiece W may be rigidly supported within the jig I for machining purposes. It should be especially noted that although the workpiece must be firmly held within the jig, the force applied by the thumb screws against the bifurcations 24 and 26 must not exceed a predetermined limit Iffsuch a limit is exceeded the bifurcations could be deformed inwardly so as to necessitate the repair or discarding of such workpiece. VAccordingly, it is essential that the force applied against the workpiece by the thumb screws P be of lirnited value. The lprf-,sent invention contemplates the provision of a novel means for limiting the value of this force. It should-be particularly noted that other forms or" workpieces W may be employed with the thumb screws P of the present invention,

the tube T with its front end fl'abutting one side of the workpiece W; spring means S interposed between the tube and the rod for biasing the rod towards the workpiece; a head H carried by the rear end of the tube T; and lock means L interposedbetween the head H and the tube T 'for normally keying them together for concurrent rotation relative to the jig J whereby the tube will be threaded through bore 22 and move axially toward the workpiece W. During such axial movement of the tube T towards the workpiece W, the rod R remains stationary relative to the tube and is hence driven axially rearwardlywithin the tube. After they rodv R has been lmoved a predetermined distance relative to the tube, the

lock means L is rendered inoperative and the head H will rotate freely relative to the tube while the tube remains stationary. In this manner the amount of axial force exerted upon the workpiece NV by the rod R is limited to a predetermined value.

More particularly, the tube T is longitudinally bored, having a front bore portion 32, an intermediate bore portion 34 of reduced diameter and a rear bore portion or spring cavity 36 of alarger diameter.k The rear end of the spring cavity 36 is closed lby means of a plug 38 that is threaded thereinto. This plug 38 is centrally formed with a bore 39. A sleeve 4t! is press-tted onto front portion 46 disposed within the front bore portion,

The main portion ot this abutment 32 of the tube T. element is of reduced diameter and its `rear end is formed with threads l 'which are engaged within the front portion Yof aninternally threaded collar *3113. A set screw 52 isthreadably disposed Within the collar 5l) rearwardly of the abutment-element '44. 'The collar 5G is formed with z an annular ange 55 that is slidably disposed within'the front portion of the spring cavity 36 of the tube T. The rear portion of the rod R includes a plunger 56 having Ya front end 58 of Vreduced diameter that is telescopically `received within the rear of the collar Eil. The rear end of this plunger element is formed with a blind bore 66. The rear end of 'the plunger element S6 islikewise rigidly secured to a latch 62 `of rectangular conguration. The width of lthis latch is 'slightly smaller than the width of the aligned notches t2 of the sleeve 40 of tube T. The outer opposite front edges of 4the latch are `seen to be formed with a bevel, as indicated at 64.

The spring means S consists of a helical 'compression spring that is interposed between the rear end'of lthe collar Si) and the front end ofthe plug 38 within the spring cavity 36;A With this arrangement, the collar 50 and hence the abutment element 44 or" the rod `R will Vconstantly be vbiased forwardly relative'to the tube T.

The head .H includes an externally'knurled main body 68` that 'is journaled upon the rear portion of the tube are de'ned by the shoulder existing between the tubcs bore portions 32 and 34, and the shoulder existing between j the front portion 46 of the rods abutment .element ly i T forwardly of the sleeve 40. This head H is formed with a forwardly extending, internally threaded blind bore 70. The rear end of this blind bore is closed by the rear .wall 72 of a closure element 74.v The'closure element 74 is integrally formed with a sleeve portion 76 which extends forwardly from the rear wall 72. The sleeve portion 76 is formed withV a pair of diametrically opposed, circumferentially extending aligned notches '73. The intermediate section of the sleeve 76 is formed with external threads thatengage the complementary threads formed within the blind bore 70 so as to secure the closure element 72 to the main body 68. The rear Wall.`.72 is centrally formed with a seat 84. A small helical compression spring S6 is disposed with its rear endwithin this seat 84 and its front end within the blind bore 60 of the plunger element 56 of the rod R. With this ar- Y rangement, the head H will constantly be biased rearwardly relative to the ltube T.

In operation, the parts of thethumb screw P will initially,V be disposed as .shown in Figures 2 and 5. At .this time .the latch element 62 will be positioned within the aligned.

notches 42 and 78 of the .sleeves 4t) and 76, respectively. The head H will then be `manually rotated .in a clockwise direction relative to Figure'B, and since the head .and

tube are interlocked by means of the latch element 62 .they will undergo concurrent rotation. lnthis mannerrthe tube will be threaded through the jig -bore 22 whereby the Vfront Vend Vof the rod R will Aapply pressure againsty the workpiece W. `As the tube moves axially to the right in Figure 2, the rod R will remain stationary relative to the tube .andsuch relativemovement between the Vtube and the rod will gradually cause the notches 42 of the sleeve 4t? to move away from thelatch element 62, as indicated in Figures 4 and 6.. When the latch element 62 andthe sleeve 40. vhave reached their approximate relative posi' `tions indicated'in'these.V two figures, the continued rotathe tube T, and hence axial, movement of the tube toward the workpiece W will stop. Thus, the latch element62 and the notched sleeve 40 `serve as disengageable loclcrneans between the head H and thetube T. 'The amount of axialV force applied to the workpiece W by the rod R beforeV the 'latch element 62 is cammed out of the notches 42' is determined by the adjustment of the plug 38 relative to the rear of the tube T.

Referring now to Figure v2, it should' be particularly noted that the latch element 62 .will'becomedisengaged from the sleeve 40 just as complementary abutment surfaces v'57 and 38 of the tube T and rod VR, respectively, come into contact. These abutment surfaces v37 and 88 and the main portion thereof. The engagement vof these abutment surfaces insures that the tube T and the rodV R will form a positive and unyielding connection betweenf the jig 'I `and the workpiece W.' Accordingly, the workpiece W will not vibrate relative to the jig during a ma-A chining operation. The engagement ofthe abutment surfaces 37 and S8 is made to coincide with theycamming of thel latch element 62 out ofthe notches 42 Vof sleeve 4d bythe proper adjustment of the Vrod element 4d relative to the collar Sil. This adjustmentrmay be made by un threading theclosure element 74 Vfrom the main'body ed of the head H and removing the plu-nger element'56, so.

as to provide access to the set screw 52. As indicated in Figure 3, a pair of holes 86 may be formed in the rear closure lrnernber for receiving a .suitableV Spanner vwrench (not shown).

When it is desired to backthe thumb screw P awa-yfrom the workpiece, the head H'will be rotated lin the opposite or counter-clockwise direction 'relative to Figure 3; The latch element 62 will be rotated in unison with'the head because of the engagement of the ends thereof with the notches 78 of the latters sleeve 7 6. During such rotation of the latch element, its blur: edges 65 will engage the sides of the notches 42 of the tube sleeve 40. These blunt edges 65 will not serve to cam the latch element out of the notches 42 and instead the latch element will impart rotation to the sleeve 40 and hence the tube T. The tube T will thus be threaded out of the jig bore 22 and the rod R moved away from the workpiece W.

Referring now to Figures 8, 9 and l0, the second form of thumb screw with overload release P' embodying the present invention comprises an externally threaded tube Tb shown threaded into the bore 22 of a jig; a rod Rb coaxially slidably disposed within the tube Ta with its front end 90 abutting one side of a workpiece W; spring means Sa interposed between the tube and the rod for biasing the rod towards the workpiece; a head Hb carried by the rear of the tube; and lock means La interposed between ethe head and the tube for normally keying them together for concurrent rotation relative to the jig J whereby the tube will be moved axially towards the workpiece W.- In this form of the invention the tube Ta is formed with a coaxial longitudinally extending bore 92. The front portion of this bore 92 is of enlarged diameter and defines a springcavity 94. The rear portion of the tube is formed with an annular recess 96 and forwardly of this recess the tube is formed with a notch 98 that extends radially inwardly' from one side of the tube to a point somewhat beyond the center thereof. The rear extremity of the tube is formed with a lock surface 100 which tapers radially inwardly and rearwardly.

The rod Ra includes a main portion HB2 and an abutment element 104 of enlarged diameter. The abutment element 194 is slidably disposed within the front portion of the spring cavity 94 of the tube Ta. The spring means Sb is. a helical compression spring that is interposed between the rear surface of the abutment element 104 and the rear end of the spring cavity 94. The rear end of the rods main portion 162 is formed with external threads 105.

The head Ha is formed with a rearwardly extending blind cavity 19S. The rear portion of this cavity 108 is formed with a radially inwardly and rearwardly extending lock surface 11) that is complementary to and normally seated upon the tapered lock surface i) of the tube Ta. These two lock surfaces comprise the lock means Lb. The head Ha is centrally formed with an internally threaded bore 112 which is threadedly engaged with the threads 105 of the rod R. A lock nut 114 is carried by the rear extremity of the rod Re for locking the rod and the head together. A stop screw'116 is threadedly secured within a threaded bore 113 formed in the front portion of the head. The radially inner portion of this stop screw 116 is disposed within the semi-annular groove 96 of the tube Tb. This stop screw 116 retains the head Ha upon the tube Tb while permitting limited relative axial movement to take place therebetween. A ball element 120 is disposed within the notch 9S of the tube Ta.

ln operation, the parts of the thumb screw P' will initially be disposed as indicated in Figure 8. As the head Ha is rotated in a clockwise direction relative to Figure 9, it will initially impart concurrent rotation to the tube Tb ecause of the rotation-resisting engagement of the lock surfaces 13E and. il@ whereby the tube will be threaded into the bore 22 of the jig l. The tube Ta will thus be moved axially to the right toward the workpiece W. Since the rod Rb and hence the head Ha will remain stationary relative to the tube Tb during the latters movement toward the workpiece W, the tapered lock surface 160 of the tube will gradually move way from the complementary tapered lock surface 110 of the head to the right, as indicated in Figure lO. When the lock surfaces 160 and 110 have been suiiiciently separated, the head Hb may rotate freely relative to the tube Ta and 6 accordingly the latter will stop its axial movement to the right.

Referring now to Figure 9, rotation of the head Hb in a clockwise direction so as to screw the tube T toward the workpiece W will not be resisted by the ball element 120. When, however, the head is rotated in a counterclockwise direction the ball element 129 will act as a cam within the notch 98 so as to lock the head to the tube and thereby permit the tube to be backed away from the workpiece W. Thus, the ball element 126 and the notch 93 serve as a backout means in this form of the invention. In order to adjust the amount of force required to disengage the lock surfaces and 110, the rear end of the rod Rb is formed with a slot 122. This slot may be engaged by a screwdriver after the lock nut 114 has been backed o so as to adjust the relative axial positions of the rod and the tube and thereby change the etfective force of the spring Sa. When the rod has been adjusted the lock nut 114 is again tightened.

Referring now to Figures 1l through 14, the third form of thumb screw with overload release P" embodying the present invention comprises an externally threaded tube Tb shown threaded into the bore 22 of a jig l; a rod Rb coaxially slidably disposed within the tube Tb with its front end 124 in abutment with one side of the workpiece W; spring means Sb interposed between the tube and the rod for biasing the rod toward the workpiece; a head Hb carried by the rear end of the tube T; and lock means Lb interposed between the head and the tube normally keying them together for concurrent rotation relative to the jig J whereby the tube will be moved axially towards the workpiece. The tube Tb is formed with a longitudinal bore 126 having a front portion of enlarged diametery deiining a spring cavity 128. The rear end of the tube is rigidly secured as by a pin 130 to a sleeve, generally designatedY 132. The rear end of the sleeve 132 is formed with a plurality of axially extending splines 134. A notch 136 is formed in the sleeve for receiving a backout roller 138. The sleeve 132 is formed with a main bore 140 and a smaller bore 142 disposed rearwardly thereof. An annular groove 144 is formed in thefront portion of the sleeve for retaining a resilient seal 145,

The rod Rb includes a main body 146 and an abutment element 143 integrally formed on the front portion of the main body. This abutment element 14E is axially sldably disposed within the spring cavity 12S of the tube. The spring means Sb consists or a helical compression spring that is interposed between the rear end of the abutment element 14S and rear end of the spring cavity 12S. The rear end of the rods main body 146 is formed with external threads 152. These threads are engaged with the threads 154 of a collar member 156. The collar includes an annular ilange 15S which is disposed within the rear portion of the main bore 141i of the tube sleeve 132. The head Hb is formed with a rearwardly extending blind cavity having an inner diameter slightly larger than the outside diameter of the sleeve 132. The rear portion of this cavity is formed with a plurality of axially extending splines 162 which are complementary to the splines 134 formed on the sleeve 132. These splines 134 and 136 comprise the lock means Lb. The rear wall 164 of the head is centrally formed with an internally threaded bore 166. This bore 166 is threadably engaged with external threads 167 formed on the collar 156. A lock nut 168 is carried by the rear end ofthe collar 156.

In operation, the parts of the thumb screw P will initially be disposed in their position of Figures ll and 12. As the head Hb is rotated in a clockwise direction relative to Figure l2, it will initially impart concurrent rotation to the sleeve 132 and hence the tube Tb by virtue of the inter-engagement of the splines 134 and 162. As the tube Tb is threaded towards the workpiece W, the rod -Rb and hence tthe head Hb will remain stationary relative tothe tube and its sleeve 4132. Accordingly,

the splines 162 of the head Hb will gradually be moved to the left until they are disengaged from the splines- 134 of the tubes sleeve 132, as indicated in lFigure 13. At this time the head will be free to rotate relative to the sleeve 132 and hencev the tube Tb. lReferring -to vFigure l2, in order to back the tube Tbr out of the bore 22 away from the workpiece, the head 'Hb is rotated in a counterclockwise direction. During such counter-clockwise rotation the backout roller 158 wil-l act as a cam within ythe notch 136 so as to cause the head to effect concurrent rotation'of the sleeve 152 and hence of Athe tube Tb.

1n order that the tube Tb and the rod Rb may provide a Apositive and uny-ielding connection between the jig J and the V-worlopiece WV, the rear surface of the ange 158 of collar'ti defines an abutment ysurface 170 which engages a complementary abutmentsu-rface 172 defined by the shoulder hetweenrthe bores 141 and 142 of the sleeve 132, as indicated in Figure 13, when the splines 134 and l16.?. are disengaged. Adjustment of the force required to elect the disengagement of the splines `1354 and 162 may be made by threading or unthreading the .rod Rb Y relative to the collar 156 to thereby change.` the elective Referring now to Figures through 19, the preferred form of thumb screw with overload release P" embodying A the 'present invention comprises an externally threaded tube Tc shown threaded into the bore 22 of Ya jig I; a rod Rc coaxially slidably disposed within the tube Tc with its front end 186 abutting one side of a workpiece W; spring means SC interposed between the tube and the rod for biasing the rod toward the workpiece; a head HC carried by the rear end of the tube; land lock means Lc interposed between the head kand the'tubc normally keyingthemtogether for concurrent rotation relative to the jig I whereby the tube will be moved axially towards the workpiece W.

in this form of the invention the tube TC is formed with a coaxial longitudinally extending bore 182 having a front portion 184 that is slightly larger in diameter than the main portion thereof. The rear end of the Vtube is rigidly secured to a sleeve member 186 that is -centrally formed with'a rst bore 188 which is press-'fitted to the rear end of the tube, and a second bore 190 disposed rearwardly a front'portion 196 that is of slightly larger diameter and Y au externally threaded rearV post "198; The rod portions 195 and 196 Vare axially slidahly disposed within the bore portions 182 and 134, respectively, Vof the tube. A collar 28! is threadedly Vsecured to the vpost 198 and is retained thereon by a lock nut 202. The collar 200 includes an annular harige 204 formed at its rear end. The main portion of the collar 2118 is' axially slidably disposed within the bore 183 of the sleeve 186. Thespring means Sc consists of a helical'compression spring which lis interposed between the frontksurface of theplug 1192 and 'the rear ofthe annular `ilange 204 of the collar 200. With this arrangement, ther-od RU is e'onstantlybiasedforwardly Vttm/ard the workpiece W, the front surface ofthe a'nge 204 abutting the shoulder 206 dened between the bores 188 and 19d of the sleeve 186.

As shown in Figures l5 and 16, the'sleeve Vdis formedV with .a radially extending 'threaded bore 208. Thisbore 208 Ithreadedly receives a circular :guide elementll which.

8i. slidably mounts a hexagonal plunger 212.

while y.the radially inner end thereof is formed with a cav ity 216. A spring element 218 disposed in the bore 188- of uthe sleeve has an end portion 221) that seats within the cavity 216 of the plunger. With this arrangement,

the plunger 212 is constantly biased radially outwardly relative to the sleeve 136.

The head includes a cylinder 222 having a slightly larger inside diameter than the outside diameter of the sleeve l186. The front end ofjthis ycylinder 222 is integrally formed with a radially inwardly extending flange head relative to the sleeve. a pair of diametrically opposed axial bores 232 which mount :the frontportion of alpair ofl pins 234. 'The rear portion of the latter extend into the annular space236 dened between the sleeve '186 yand the'heads cylinder '222. Y l

The Vplunger 212 and the pins v234 comprise the lock means Lc. f

Tn the operation of this form of the invention theparts of the thumb screw P" will initially bel disposed in their position of Figures l5 and 16. As the head H0 is rotatedV in a clockwise direction relative to Figure 16, it will initially impart concurrent clockwise rotation' to the sleeve 1'86Y and -hence to the tube Tc by virtue of the inter-engagement of the heads pins 234-and the rplunger 212, as shown in this figure.

plunger 212 will be moved to the right relative to the collar 260. Eventually Ythe radially inner vrend of Athe plunger 212 vwill clear the collar 200 and the plunger will be free to move radially inwardly,as indicated in Figures` 18 and V19. Continued clockwise rotation of the head ,will

cause the beveledend 214 of the plunger'212 to be-eammed radially inwardly by thepins 234, as will be apparentKV from Figures 18 and 19. The head will Vthen be'free to rotatefreely relative to the sleeve 186 and hence the tube Tc.

Referring now to Figures 16 and 19, in 'order toback Vin'uence of the spring 218. Accordingly, the counter-` clockwise -rotation ofthe head Hc will be transferredrtoj the sleeve -186andhence to the-tube "l`c whereby theilatter will be backed out of the jig bore 22.

In order that the tube Tc and the vrod VR-c Lmay provide a'positive and unyielding connection between the jig I and-v the workpiece W,`the shoulder between the rod port-ions and 196 .defines an vabutment surface `240 which .en-4

gages a complementary abutment surface 242 defined -by the shoulder existing between the tubes bore portions-18`2 and 184 when the radially inner, end of the plunger 212 clears the collar 200. The engagement of the abutment surfaces 240 and ,242 may be made to coincide with the radially inward movement of the plunger 212 after it has been cleared bythe collar 200 by the proper .axial adjustment of the 'latter relative to the vpost 198 ofthe rod Rc.

To carry out this adjustment the lock 'nut 202 should 'first be backed off. Adjustment of the axial force exerted by the rod Rc upon the workpiece W before the plunger 212 lclears the collar 200 :maybe made by threadingfor unthrcading the plug 192 relative to the -bore190 of-.the head Hc. f

It should he particularly observed that each 0f the The radially outer end of this yplunger 212 is angled as indicated at 214,

The tube will thus be threaded into ther bore 22 and the rod Re will engage Vthe workpiece W. The rod will thereafter vremain stationary while the tube con#y tinues to ymove axially tothe right relative to Figure. V15. During such tube movement the sleeve 186 and hence the During such 'counter-'clockwise rotation kthe right-V aforedescribed forms of thumb screws embodying the present invention have one feature in common, i. e. in each case the sensing of the amount of axial force exerted upon the workpiece takes place at the point of contact of the screw with the workpiece. In this manner the eiect of friction between the threads of the pressure screw and the jig bore is completely eliminated. Accordingly, very accurate results are consistently obtainable.

It should also be observed that although four diiferent forms of disengageable lock means between the rod and the head have been shown and described hereinbefore, it is within the scope of the invention to provide other forms of lock means. It should likewise be observed that various other modications and changes may be made with respect to the speciic construction of the thumb screws with overload releases shown and described herein without departing from the spirit of the invention or the scope of the following claims. Y

I claim:

1. A thumb screw with overload release for use with a first object formed with a threaded bore and a second object that is positioned adjacent said rst object inline with said bore, comprising: an externally threaded tube threadable within the bore of said tirst object; a rod axially slidably carried within said tube for engaging said second object; a head; spring means interposed between said tube and said rod tending to effect their axial separation; and lock means normally interconnecting said head and said tube in order that they may undergo concurrent rotation, said lock means being rendered inoperative upon the occurrence of a predetermined amount of axial movement of said tube relative to said rod against the force exerted by said spring means.

2. A thumb screw with overload release as set forth in claim l having means for adjusting the force exerted by said spring means.

3. A thumb screw with overload release as set forth in claim 2 wherein said tube and said rod are formed with complementary abutment surfaces that interengage upon predetermined axial movement between said tube and rod so as to restrain further movement from taking place therebetween.

4. A thumb screw with overload release for use with a first object formed with a threaded bore and a second object that is positioned adjacent said first object in line with said bore, comprising: an externally threaded tube threadable within the bore of said rst object; a rod axially slidably carried within said tube for engaging said second object; a head carried by said tube; spring means interposed between said tube and said rod tending to effect their axial separation, and lock means normally interconnecting said head and said tube in order that they may undergo concurrent rotation in one direction, said lock means being rendered inoperative upon the occurrence of a predetermined amount of axial movement of said tube relative to said rod against the force of said spring means; and backout means interposed between said head and said tube for elfecting their interconnection when said lock means is inoperative whereby they may be concurrently rotated in the opposite direction.

5. A thumb screw with overload release for use with a rst object formed with a threaded bore and a second object that is positioned adjacent said first object in line with said bore, comprising: an externally threaded tube member threadable within the bore of said rst object; a rod member axially slidably carried within said tube member for engaging said second object; a head disposed at the rear of said tube member; a sleeve member having a circumferentially extending notch formed on one of said members; a radially extending latch formed on the other of said members; and, resilient means interposed between said members tending to effect their axial separation and normally retaining said latch within said notch with one of its edges abutting one side of said notch in order that said members may undergo concurrent rotation, said latch becoming disengaged from said notch upon the occurrence of a predetermined amount of axial movement of said tube member relative to said rod member.

6. A thumb screw with overload release as set forth in claim 5 wherein said tube and rod members are formed with complementary abutment surfaces that interengage when said latch is disengaged from said notch so as to restrain further axial movement from taking place between said members.

7. A thumb screw with overload release as set forth in claim 6 wherein said one edge of said latch is formed with a bevel and the opposite edge thereof is straightsided.

S. A thumb screw with overload release as'set forth in claim 7 where said'resilient means includes a spring and said pressure screw includes means for adjusting the force exerted by said spring.

9. A thumb screw with overload release for use with alirst object formed with a threaded bore and a second object that is positioned adjacent said irst object in line with said bore, comprising: an externally threaded tube member threadable within the bore of said first object; a rod member axially slidably carried within said tube member for engaging said second object; a head secured to said rod member; a radially inwardly and rearwardly extending lock surface formed upon said tube member; a complementary radially inwardly and rearwardly extending lock surface formed upon said head; and, resilient means interposed between said members tending to effect their axial separation whereby said lock surfaces will normally be interengaged in order that said members may undergo concurrent rotation, said lock surfaces being disengaged upon the occurrence of a predetermined amount of axial movement of said tube member relative to said rod member.

ll. A thumb screw with overload release as set forth in claim 9 wherein said head includes a bore that encompasses the rear portion of said tube member, the rear portion of said tube member is formed with a notch that extends radially inwardly from one of its sides, and a ball element is disposed Within said notch.

l1. A thumb screw with overhead release as set forth in claim l0 where said resilient means includes a spring and said pressure screw includes means for adjusting the force exerted by said spring.

l2. A thumb screw with overload release for use with a first object formed with a threaded bore and a second object that is positioned adjacent said first object in line with said bore, comprising: an externally threaded tube member threadable within the bore of said first object; a rod member axially slidably carried within said tube member for engaging said second object; a head disposed at the rear portion of said tube member and secured to said rod member; axiallyextending splines formed on said tube member; complementar] axially extending splines operatively connected to said rod member; and, resilient means interposed between said members tending to elect their axial separation whereby said splines will normally be interengaged in order thatsaid members may undergo concurrent rotation, said splines being disengagedl upon the occurrence of a predetermined amount of axial movement of said tube member relative to said rod member.

13. A thumb screw with overload release as set forth in claim l2 wherein said tube and rod members are formed with complementary abutment surfaces that interengage when said splines are disengaged so as to restrain further axial movement from taking place between said members.

14. A thumb screw with overload release as set forth in claim 13 wherein said head includes a bore that encompasses the rear portion of said tube member, the rear portion of said tube member is formed with a notch that extends radially .inwardly from ene of its `sides, and

a hackout roller is disposed within said notch.

l5. `Athumb screw with overload release for use Ywith a first object formed with a threaded bore and a secondV o'bieet that lis positioned adjacent said first object in line with said bore, comprising: an externally threaded tube tending piu secured to said head and kdisposed Within ksaid space; a .radially k extending passage formed in said tube'member; a plunger slidably disposed in said passage and having its Vradially youter portion constantly biased into said annular space, the radially outerY portion of said plunger :being 'formedsvith a bevel; .a yfollar formed on said rod member for abutting jthe radially kinner end Vof said plunger :whereby said pin will lengage the beveled portion of said plunger .and cause rotation of said lhead to effect .concurrent rotation of said tube .ndernberg-,ani resilient means interposed between said tube and rod members :tending to effect .their-axial separati@ 'WllQreby said colla-r will normally be radially aligned -with said plunger, said collar moving `out Vof alignment with said plunger upon the occurrence of a predetermined amount ofaxial movement of said 'tube member relative lto said rod member. l

lr6. A thumb screw with overload release Vas set forth in claim 15 wherein said tube and rod members are. formed with complementary abutment surfaces that interengage. when said collar, moves out of alignment with said plunger so -as to .restrain further yaxial movement from taking place between said members.

i7. A thumb screw with overload release asset forth in vclaim '16 wheresaid resilient means includes a spring and said pressurescrew includes means for adjusting the force .exerted fbysaid spring. i f v .Reiereliees Cited inthe UNITED STATES PATENTS .lfe of this patent Y 

